Surgeons have replaced 75 percent of a man’s skull with a custom-designed polymer cranium constructed with a 3-D printer. The surgery took place on March 4 and is the first U.S. case following the FDA’s approval of the implants last month. The patient’s reason for needing such extensive replacement surgery has not been revealed.

Similar surgeries may follow in other cases where sections of the skull are removed because the brain has swollen during a surgery or after an accident, says Scott ...